Alzheimer's Disease is the most common neurodegenerative disease worldwide, but significant gaps in pathophysiological understanding have hampered development of disease-modifying therapies. In Alzheimer's disease, neurophysiological function is impaired, with gamma frequency oscillations - thought to be essential for higher-order cognitive processes - disrupted in both patients and animal models. However, the mechanisms driving these disruptions are unclear and, in particular, the role of neuroinflammation in these changes is poorly understood. In this study, we investigated neuronal network dynamics in acute brain slices from APP/PS1 transgenic mice. Gamma frequency oscillations had significantly reduced amplitude in APP/PS1 brain slices at 9-11 months, accompanied by an increase in beta frequency power and heightened epileptiform activity. This is suggestive of a slowing in neuronal oscillations, considered a neurophysiological hallmark of Alzheimer's disease. Immunohistochemical analysis revealed a reduction in parvalbumin- and somatostatin-positive inhibitory interneuron populations. Treatment with gabazine demonstrated increased network sensitivity to GABAA receptor antagonism, further indicating compromised inhibitory control in APP/PS1. As these altered oscillatory dynamics correlated with microglial reactivity, we hypothesised a causal role for microglia. Administration of the CSF1R inhibitor GW2580 reduced microglial proliferation, attenuated development of the disease-associated microglial phenotype and partially rescued synaptic loss; but, had no significant impact on amyloid plaque burden or cognitive deficits. Unexpectedly, GW2580 treatment exacerbated neuronal network hyperactivity and the incidence and complexity of epileptiform activity. Microglia in GW2580-treated mice showed reduced CD68 expression and decreased engulfment of synaptic elements, potentially facilitating the persistence of hyperexcitable synapses. These findings support a role of microglia in regulating neuronal network homeostasis and caution against indiscriminate suppression of microglial activity in Alzheimer's disease. Therapeutic strategies targeting microglia must account for their homeostatic functions to avoid adverse effects on neuronal network stability.

Infections have long been implicated as causative factors in Alzheimer's disease (AD). Multiple studies have further suggested a key role for herpesviruses, such as cytomegalovirus (CMV). Using transgenic 3xTg-AD mice, we demonstrate that systemic infection with the β-herpesvirus murine CMV (MCMV) accelerates the development of cognitive decline, tauopathy and synaptic loss in the hippocampus, all of which are key features of AD. Accelerated disease progression after infection was associated with substantial lymphocyte infiltration into the brain, dominated by MCMV-specific effector memory CD8+ T cells expressing CXCR3. T cell receptor analyses revealed that clonally diverse virus-specific CD8+ T cells were selectively recruited into the brain during the development of AD. T cell depletion or treatment with the antiviral drug valganciclovir during chronic infection reduced lymphocytic infiltrates in the brain and reversed cognitive decline. These data provide a mechanistic link between chronic viral infections and the development of AD.

The frontotemporal language network is functionally specialized for language processing and activates only to linguistic processing. Whether other regions can acquire this function is a key issue in neuroplasticity as it remains unclear whether cortical regions can ever change their specializations. Deprived sensory cortices, i.e., visual cortices of the blind and the auditory cortices of the deaf, have been the strongest candidate for this. These regions cannot perform their original function and have all the impetus to change. Indeed, numerous studies have shown their activation during various language tasks and have suggested that these regions acquire linguistic processing functions. However, activation during language tasks does not imply activation to linguistic processing. These activations could have been due to the accompanying sensory processing or domain-general task demands. We had congenitally blind, deaf, sign-language-using children of deaf parents, and sighted and hearing controls, do two language tasks. Blind participants additionally did a series of cognitive control tasks. We found that neither the visual cortices in the blind nor the auditory cortices in the deaf activated to linguistic processing. Visual cortices in the blind, like the multiple-demand frontoparietal regions, activated only when the language task was accompanied by domain-general demands, and not when language was to be processed in their absence. In contrast, the canonical language regions activated during any linguistic processing, regardless of the accompanying task demands. Crucially, the visual cortical voxels that activated during the demanding language task also activated in response to a host of non-linguistic cognitive control demands but not when linguistic processing occurred in the absence of task demands, showing that these regions were indeed activated by domain-general demands. Likewise, auditory regions in the deaf showed no activation to linguistic processing, and instead activated to sensory processing demands. Linguistic processing in them was again limited to the canonical language regions. Deprived sensory cortices, contrary to many claims, do not become language regions.

Alzheimer's Disease (AD) is an age-dependent neurodegenerative disorder and represents the most common type of dementia, increasing in incidence at an alarming rate in the aging population. The hallmarks of the disease are amyloid plaque accumulation, microglia and astrocyte activation, and loss of presynaptic structure leading to cognitive decline. Recently, oligodendrocyte (OL) and myelin abnormalities have emerged as important contributors to the pathogenesis of AD. In normal brain homeostatic conditions, OL maintain neuronal health through myelin axon interactions and by supplying neurotrophic and metabolic support. How strengthening OL function may support neuronal health in AD neurodegeneration remains to be fully characterized and represents a gap in knowledge and a missed therapeutic opportunity. This study sought to examine how myelin and OL may improve neuronal deficits associated with AD. We have generated a novel mouse model (AD/cKO) by crossing the AppNL-G-F mouse, an established AD model, which carries three human AD mutations in the mouse App gene, with the FusOLcKO whose OL depleted of Fus (Fused in Sarcoma) produce thicker myelin associated with greater cholesterol biosynthesis. We evaluated spatial memory function with standardized cognitive testing. We evaluated microglia density and state, astrocytic activation and toxic phenotype, myelin density, cholesterol content, amyloid plaque burden, presynaptic structures, and neuronal hypoxic and oxidative damage in the hippocampus and cortex. We characterized the transcriptome of AD/cKO hippocampal OL compared to AD by using single-cell transcriptomic studies. Spatial working memory was fully preserved in the aged AD/cKO mouse relative to the AD mouse. This outcome was associated with reduced neuronal oxidative damage, preserved presynaptic structures at the amyloid plaque niches, and a shift in microglia state at the niches in both hippocampus and cortex. In contrast, amyloid plaque burden and microglia density were decreased in the hippocampus but not in cortex, uncoupling the neuronal and microglia effects from the amyloid burden. Fus dependent myelin increase was present in both hippocampus and cortex. Single-cell transcriptomics of AD/cKO hippocampal OL revealed upregulation of energy metabolism and antioxidant genes, suggesting a role of OL enhanced energy metabolism in mediating protection of neurons and affecting microglia state in AD pathology. This work provides new insight into how oligodendrocytes may protect neurons in AD, communicate with other glial cellular players, and point to potential targets for disease intervention aimed at slowing AD progression.

Propionic acid (PA), a microbial-derived short-chain fatty acid, contributes to intestinal barrier integrity, systemic immune regulation, and neuronal function. Individuals with multiple sclerosis show reduced PA levels, and open-label data have suggested beneficial immunomodulatory and clinical effects of supplementation. The Multiple sclerosis And DisAbility Improvement (MADAI) trial was a randomized, double-blind, placebo-controlled, single-centre, phase 2b study designed to evaluate the efficacy and safety of PA as an add-on therapy in adults with clinically stable multiple sclerosis. Between April 5 and 29 May 2024, 101 adults (64% women; mean age 45 years) were randomly assigned in a 2:1 ratio to receive PA 500 mg twice daily or matching placebo for 90 days. The primary outcome was the change in serum neurofilament light chain (sNfL) concentration, a biomarker of neuroaxonal damage, adjusted for age, body mass index, creatinine, and baseline sNfL. Secondary outcomes included physical and cognitive performance measures and patient-reported outcomes, including fatigue and quality of life scores. sNfL levels were significantly reduced in the PA group {-17.9%; from 9.77 pg/ml [95% confidence interval (CI) 9.00 to 10.60] to 8.02 pg/ml (95% CI 7.36 to 8.73); mean difference 1.75 pg/ml (95% CI 0.9 to 2.6); P = 0.000025}, while no significant change was observed in the placebo group. The adjusted mean difference in sNfL levels between the PA and placebo groups at follow-up was 0.91 pg/ml (95% CI 0.02 to 1.79; P = 0.045). Reductions in sNfL were also observed among participants in the PA arm receiving moderate-to-high efficacy disease-modifying therapies (n = 41; P = 0.0001), including those on anti-CD20 treatment (n = 27; P = 0.0005). There was a trend towards improvement in motor fatigue in the PA group. No serious adverse events related to the study medication occurred. PA supplementation was well tolerated and associated with significant reductions in sNfL, suggesting attenuation of neuroaxonal injury in multiple sclerosis. These findings support further evaluation of PA as an add-on treatment in larger, long-term studies.

WOREE and SCAR12 syndromes are rare neurodevelopmental disorders caused by WWOX mutations, severely impairing brain development. The pleiotropic nature of WWOX complicates identifying specific mechanisms, thus, the specific molecular pathways affected by WWOX deficiency and how they contribute to disease pathogenesis remain largely unknown. Using neural organoids derived from a broad iPSC cohort, including wildtype iPSCs, CRISPR-edited isogenic WWOX-knockout lines, and patient-derived lines, we applied molecular profiling and single-cell transcriptomics to map the early neurodevelopmental pathways disrupted upon loss of WWOX. We identified radial glial cells (RGs) as preferentially affected, with disrupted cell cycle dynamics leading to an accumulation of cells in the G2/M and S phases, overexpression of the proto-oncogene MYC, and concomitant reduction in neuronal generation. Patient-derived organoids exhibited milder phenotypes compared to knockout organoids, showing functional neuronal impairments like hyperexcitability and delayed differentiation rather than RG dysfunction. Remarkably, gene therapy restored neuronal function, normalizing hyperexcitability and promoting maturation, without disturbing RG populations. We propose a model in which WWOX mutations impair neurogenesis via RG through cell-type specific dysregulation of the MYC and Wnt signaling pathways. These insights highlight potential therapeutic strategies for WWOX-related disorders and open avenues for interventions targeting these key molecular pathways.

Variants in SMPD4 cause severe neurodevelopmental disorders characterized by microcephaly, simplified gyral patterns, and cortical malformations in humans, yet Smpd4 knockout mice exhibit minimal cortical abnormalities, displaying phenotypes primarily restricted to cerebellar defects. This striking species-specific disparity has hindered understanding of the cellular and molecular mechanisms underlying SMPD4-related cortical pathology due to the lack of appropriate gyrencephalic animal models that accurately recapitulate human brain development. We utilized in utero electroporation combined with CRISPR-Cas9 genome editing technology to efficiently knock out Smpd4 in the developing gyrencephalic neocortex of ferrets at embryonic day 34. Ferrets were analyzed at postnatal days 1, 2, 6, and 16 using immunohistochemistry, live-cell imaging, and single-cell RNA sequencing to comprehensively characterize the cellular and molecular consequences of SMPD4 deficiency. SMPD4-deficient ferret cortices successfully recapitulated key human phenotypes, exhibiting markedly reduced progenitor cell proliferation with significantly prolonged mitotic duration. Quantitative analysis revealed a profound reduction in basal intermediate progenitors and decreased neuronal output. Mechanistically, loss of SMPD4 compromised nuclear envelope integrity, disrupted mitotic spindle orientation leading to aberrant cell division patterns, impaired primary cilia formation, and substantially reduced intermediate progenitor morphological complexity. Additionally, Smpd4 knockout induced severe migration defects in cortical neurons, with many neurons failing to reach their appropriate cortical layers. Single-cell RNA sequencing analysis of over 20,000 cells from control and Smpd4 knockout cortices revealed that SMPD4 deficiency significantly reduced intermediate progenitor cell numbers and caused widespread dysregulation of genes previously associated with human lissencephaly, simplified gyration, microcephaly, developmental delay, and epilepsy. Gene ontology enrichment analyses identified disrupted pathways involved in cell cycle regulation, neurogenesis, chromosome organization, apoptosis, and neuronal migration. These findings provide critical mechanistic insights into how SMPD4 deficiency disrupts cortical development through impaired intermediate progenitor generation and neuronal migration, establishing ferrets as an invaluable gyrencephalic model system for investigating SMPD4-related neurodevelopmental disorders. This model offers significant translational potential for understanding human cortical malformations and developing therapeutic interventions for affected patients.